This invention relates to apparatus for detecting incident radiation. More particularly, it is concerned with semiconductor radiation detecting devices.
In conventional semiconductor radiation detecting devices the electric field generated by a rectifying junction is used to separate and to collect the charge carriers (electrons or holes) produced in the semiconductor material by the absorption of incident radiation. This action requires that the radiation be absorbed by the semiconductor material at or near the junction, so that the electrons or holes can diffuse to it and be collected before encountering a recombination center in the semiconductor crystal. In conventional semiconductor devices the junction is parallel to and at a fixed depth below the surface which receives the radiation. Thus, the efficiency of conventional devices varies depending upon the depth of penetration of the radiation with respect to the depth of the junction. The semiconductor material of devices for detecting radiation with large penetration depths, such as high energy particles, x-rays, and gamma rays, must be prepared with extremely low impurity concentrations so that the depletion region of the junction extends to sufficient depth. In addition, conventional devices do not readily provide for distinguishing between different types of radiation nor for measuring their energies.